PROJECT SUMMARY Currently, ischemic damage to the heart cannot be repaired by conventional medical care therefore only palliative treatments exist. Stem cell transplantation is a promising strategy for therapeutic cardiac regeneration, but current therapies are limited by insufficient interaction between the regenerative cells and the injured tissue. In the last grant period, we have developed targeted nanoparticles (namely bispecific antibody- conjugated agents) to redirect circulating stem cells to the infarcted heart for therapeutic regeneration. Despite such initial success, we realize our system has some problems: (P1) We cannot fully reply on the stem cells (?seeds?) for cardiac repair. The post-injury heart microenvironment (?soil?) needs to be primed for the maximum outcome; (P2) Antibody targeting is quite specific but is fully dependent on the antigen, which are cardiac injury biomarkers that only expresses in a short period of time after injury. The current renewal proposal builds on the previous study, but represents a significant advancement, both technically and conceptually. To address P1, we reason one of the antibodies needs to be therapeutic, to combat the excessive inflammation in the heart. To address P2, we seek for agents that have broad spectrum affinity with cardiac injury. To those ends, we developed anti-IL-1 platelet mimetic (IL1-PM). The mode of action for IL1-PM is as follows: platelet vesicles serve as the carrier of our system and they have innate ability to find cardiac injury (replying on the binding motifs on platelet membranes); anti-IL-1 antibodies are currently in Phase 3 clinical trials and have demonstrated ability to neutralize inflammation and promote cardiac repair; platelet vesicles can be further loaded with stem cell-derived growth factors to aid the repair process. AIM 1: Fabricate IL1-PM and characterize its physicochemical and biological properties. We will generate IL1-PM agents by conjugating anti IL-1 antibodies onto platelet membrane nanovesicles; binding/engaging ability, toxicity, pharmacokinetics of IL1-PM will be examined in cultured cells and in healthy animals. AIM 2: Determine the therapeutic potential of mesenchymal stem cell (MSC) secretome-loaded IL1-PM in a mouse model of myocardial infarction. MI will be induced by ischemia-reperfusion. After that, MSC-IL1-PM, along with various control agents, will be delivered intravenously. Therapeutic safety and efficacy will be determined. In addition, the underlying mechanisms of such treatment will be explored. AIM 3: Translate the findings into a clinically- relevant large animal model of myocardial infarction. MI will be induced in swine via a balloon-occlusion procedure. The safety and efficacy of MSC-IL1-PM treatment will be evaluated. Our therapeutic system combines stem cell therapy (component 1) and anti-IL1 therapy (component 2), both of which have been rigorously tested and verified in clinical trials for cardiac repair. Moreover, the therapeutics will be delivered in a targetable fashion relying on the injury-finding ability of platelet binding motifs (component 3). All 3 components have been supported by strong preliminary data from our group.